不同地表倾角下台阶法施工对大断面隧道变形的影响分析

依托简浦高速公路长秋山大断面隧道工程，运用有限差分软件FLAC3D对该隧道采用三台阶工法的动态开挖进行了模拟，分析了不同地表倾角下台阶长度对隧道洞周位移的影响规律。结果表明:浅埋大断面公路隧道三台阶法施工，隧道洞周位移大小顺序为:仰拱隆起 拱顶沉降 水平收敛；不同地表倾角下，隧道拱顶沉降及仰拱隆起变化主要发生在台阶长度为4~6 m之间，说明短台阶或超短台阶法能够较好地控制隧道的洞周变形，更为适合软弱围岩大断面隧道的施工；台阶长度从10 m开始，隧道洞周位移逐渐收敛，可作为浅埋大断面隧道台阶法施工下洞周位移的"起始收敛点"；隧道地表倾角对隧道洞周位移的变化影响较大，因此，实际施工中应根据地表的不同倾角，选择更为合理的台阶长度进行施工，确保软弱围岩大断面隧道的安全施工。

Study on Effect of Bench Cut Method on Deformation of Large Section Tunnel under Different Dip Angles

Based on Changqiu Mountain large section tunnel project of Jianyang-Pujiang expressway, the dynamic excavation of the tunnel with the method of three steps is simulated by the finite difference software FLAC3D, the influence of the step’s length on the peripheral displacement of tunnel under different dip angles is analyzed. The results show that under three steps’method construction of shallow buried large section highway tunnel, the order of the peripheral displacement of the tunnel is that:inverted arch uplift vault settlement horizontal convergence; The variation of the vault settlement and the inverted arch uplift of the tunnel are mainly between the step length of 4 m and 6 m, it is shown that the short step or the ultra short step method can well control the peripheral deformation of the tunnel, which are more suitable for the construction of large-scale tunnel with weak surrounding rock; the peripheral displacement of the tunnel are gradually converged from 10 m of the step’s length, so 10 m can be used as the’initial convergence point’ of the peripheral displacement of shallow buried large section tunnel under the step method construction. The different dip angles of tunnel have great influence on the change of tunnel’s peripheral displacement, therefore, in the actual construction, the more reasonable step length should be chosen to ensure the safety construction of the large section tunnel according to the different surface dip angles.